Investigating the Deinking of Polyethylene Post-Consumer Waste Flakes Using Industrially Applicable Surfactants

In recycling of plastic packaging, the deinking of post-consumer waste (PCW) is a key technology to achieve high-quality recyclates that can be used in demanding applications. Removing printing inks minimises the contamination in the mechanical recycling process, enabling the production of (semi)-transparent recycled films with low odour and fewer defects. While the deinking of uniformly printed model films is thoroughly researched and the general mechanism well understood, these findings are not readily transferable to industrial implementation on household PCW. This study systematically investigates the deinking of household PCW flakes using industrially available surfactants. Deinking parameters (water temperature, washing time, lye concentration) are varied with no surfactant added as well as for four industrially available surfactant formulations. The deinking efficiency is determined via an image-based statistical analysis. Via a multiple linear regression, median grey values of the experiments allow insights into the deinking mechanism of PCW flakes. Depending on the surfactant and deinking parameters, either the hydrolysis of the binding agent by sodium hydroxide (NaOH) or the surfactant-based decrease of interfacial energy on the printed surface proved dominant for the overall deinking mechanism.